Charging warning light
Discussion
Buzzlt said:
Nope, without the light I doubt the battery will charge at all. The light is used as a resistance to agitate the alternator to switch on. Replace the bulb before you go anywhere. Sorry but thems the breaks!
I hear what you say, and I was initially worried about that myself, but the battery does charge, but it needs a stab of around 3500 rpm to get ithe alternator to start charging it. I've done a good few hundred miles (some with the lights on) since the bulb blew. I was just wondering if it was coincidence that it needed more rpm to get it going - or whether something else was amiss. Edited by Buzzlt on Friday 10th June 20:39
Does anyone know what the wattage of the replacement bulb should be?
NaCl said:
If the battery warning bulb fails, does it mean the revs initially need to go higher to get the alternator to start charging the battery?
That's it exactly. Without the current through the no-charge warning lamp to energise it, you'll be relying on the relatively weak residual magnetism to generate enough power to boot-strap the field.To replace the lamp you'd want about 30-40 Ohms resistance which works out to about 3-5 Watts.
NaCl said:
Thanks everso.
If I go slightly higher on wattage, could I get the alternator to kick in as soon the engine starts and runs at tickover - like a normal car?
That seems reasonable, but I wouldn't make any drastic changes. I do remember my S2 needed quite a good blip to get it charging in the morning, whereas I can crank the V8S over with the throttle closed and it will start charging as soon as it comes up to idle.If I go slightly higher on wattage, could I get the alternator to kick in as soon the engine starts and runs at tickover - like a normal car?
NaCl said:
Thanks everso.
If I go slightly higher on wattage, could I get the alternator to kick in as soon the engine starts and runs at tickover - like a normal car?
Yes, I added an extra 2.2 watt bulb in parallel with the existing bulb and the alternator cuts in at 1300 rpm. If I go slightly higher on wattage, could I get the alternator to kick in as soon the engine starts and runs at tickover - like a normal car?
Much more neighbourly at 6:30 in the morning when I'm going to work. Not that the S3 really has a stealth mode!
Sorry to resurrect an old post...but needs must...
After putting up with no battery warning light on the dash for a while, I decided to have mess around and try to put it right.
I've found that:
1) the bulb was actually good
2) there is 12v to the bulb when the igntion is turned on
3) there is continuity from the bulb to the small terminal on the alternator
4) the bulb illuminates if I take the same wire off the alternator terminal and earth it (as you'd expect, I suppose given the above)
So my guess is that there is something up with the alternator.
It starts to charge the battery fine once the engine has been revved to about 3000 rpm and the voltmeter comes off the red up to 13-14 volts. (I've done a good few miles with the lights on so I know the batter is actually charging)
There's a small black box screwed to the back of the alternator with a solitary wire to a terminal in the casting. I've no idea what it is (some kind of capacitor / suppressor?) Could that be the problem, or is it more likely to be something inside the alternator? - maybe a bosted wire somewhere?
I seem to remember that when I was taking the cables off ages ago now (to get the alternator off so I could access the front right spark plug!) the small threaded terminal actually turned a few times before the nut started to come undone. Maybe the wire inside broke off the terminal?
Anyroadup, apologies for the long-winded blah...any help / observations appreciated
After putting up with no battery warning light on the dash for a while, I decided to have mess around and try to put it right.
I've found that:
1) the bulb was actually good
2) there is 12v to the bulb when the igntion is turned on
3) there is continuity from the bulb to the small terminal on the alternator
4) the bulb illuminates if I take the same wire off the alternator terminal and earth it (as you'd expect, I suppose given the above)
So my guess is that there is something up with the alternator.
It starts to charge the battery fine once the engine has been revved to about 3000 rpm and the voltmeter comes off the red up to 13-14 volts. (I've done a good few miles with the lights on so I know the batter is actually charging)
There's a small black box screwed to the back of the alternator with a solitary wire to a terminal in the casting. I've no idea what it is (some kind of capacitor / suppressor?) Could that be the problem, or is it more likely to be something inside the alternator? - maybe a bosted wire somewhere?
I seem to remember that when I was taking the cables off ages ago now (to get the alternator off so I could access the front right spark plug!) the small threaded terminal actually turned a few times before the nut started to come undone. Maybe the wire inside broke off the terminal?
Anyroadup, apologies for the long-winded blah...any help / observations appreciated
Yep the little black box is a capacitor for suppression. See what happens with it disconnected, pretty sure you don't need it. If you still have the same problem look for a new alternator repair pack for you alternator - probably only a tenner on the bay and much cheaper than a new alternator !
No idea what alternator you have I'm afraid, expect like on most cars there are a few different types fitted.
I think from memory the capacitor is normally a 0.1microfarad which is mainly for suppression. In the old days also used to make a right mess of the neighbours TV as well if it was faulty :-)
No idea what alternator you have I'm afraid, expect like on most cars there are a few different types fitted.
I think from memory the capacitor is normally a 0.1microfarad which is mainly for suppression. In the old days also used to make a right mess of the neighbours TV as well if it was faulty :-)
Thanks Greg.
I've already removed the suppressor thingy to see if it made any difference - it didn't (It's a 2.2 uF).
The brushes are good - they look like the only other serviceable part. My next thought was to take the alternator apart to see if I can see if I did break the wire of the small terminal inside and maybe repair it.
Or I might just leave it alone....not sure yet.
I've already removed the suppressor thingy to see if it made any difference - it didn't (It's a 2.2 uF).
The brushes are good - they look like the only other serviceable part. My next thought was to take the alternator apart to see if I can see if I did break the wire of the small terminal inside and maybe repair it.
Or I might just leave it alone....not sure yet.
NaCl said:
My next thought was to take the alternator apart to see if I can see if I did break the wire of the small terminal inside and maybe repair it.
Sounds like the most likely cause, there are plenty of alternator strip down tutorials on the net so check those out for your type before you decide to takle it. Resolved!
Small wire from battery warning light circuit had broken inside the body of the alternator - as a result of the terminal post rotating slightly when I undid the nut (to get the alternator off to remove spark plug!).
Brighter bulb (4w) now used as the battery warning light rather than 1.2 or 1.5w or whatever TVR originally fitted. The warning light now goes off as soon as engine is started and the voltmeter goes straight up to normal. No need to rev to get it to start charging.
Result
Small wire from battery warning light circuit had broken inside the body of the alternator - as a result of the terminal post rotating slightly when I undid the nut (to get the alternator off to remove spark plug!).
Brighter bulb (4w) now used as the battery warning light rather than 1.2 or 1.5w or whatever TVR originally fitted. The warning light now goes off as soon as engine is started and the voltmeter goes straight up to normal. No need to rev to get it to start charging.
Result
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